Method and Apparatus of Delivering Upstream Data in Ethernet Passive Optical Network Over Coaxial Network

ABSTRACT

An apparatus for interconnecting a fiber-optic network and a coax network comprising a coax line terminal (CLT) configured to couple to an optical line terminal (OLT) at the fiber-optic network and a plurality of coax network units (CNUs) at the coax network and to cache data received from the CNUs and forward the cached data to the OLT upon receiving a message from the OLT that assigns a transmission cycle for a specified CNU, wherein the CLT forwards the cached data to the OLT upon receiving the message regardless of whether the cached data corresponds to the specified CNU.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Coaxial cable networks (also referred to herein as coax networks) havebeen widely deployed, e.g., in the past two to three decades. Thecoaxial cable can provide Gigabit digital bandwidth that is typicallysufficient for broadband access demand. Although Time DomainMultiplexing (TDM) Passive Optical Network (PON) based Fiber-to-the-home(FTTH) systems are emerging, due to the relatively high cost of suchsystems, coax networks are still serving many broadband customers today.To support legacy systems and save investment cost in newinfrastructure, integrating some of the coaxial cable infrastructurewith the PON infrastructure is desirable, such as connecting coaxnetwork components at the home end to PON components at the distributionnetwork and central office. Ethernet PON (EPON) is one PON technologythat uses Ethernet protocol and frames for communications and canprovide Gigabit bandwidth. EPON over Coax (EPoC) technologies are beingconsidered to integrate EPONs and coax networks and hence benefit fromboth technologies and infrastructures.

SUMMARY

In one embodiment, the disclosure includes an apparatus forinterconnecting a fiber-optic network and a coax network comprising acoax line terminal (CLT) configured to couple to an optical lineterminal (OLT) at the fiber-optic network and a plurality of coaxnetwork units (CNUs) at the coax network and to cache data received fromthe CNUs and forward the cached data to the OLT upon receiving a messagefrom the OLT that assigns a transmission cycle for a specified CNU,wherein the CLT forwards the cached data to the OLT upon receiving themessage regardless of whether the cached data corresponds to thespecified CNU.

In another embodiment, the disclosure includes a network component forinterconnecting a fiber-optic network with a coax network in a PON overcoax system comprising a receiver configured to receive data from one ormore CNUs in the coax network and a first message from OLT of the PONthat indicates a specified CNU, a buffer configured to cache thereceived data, a processor configured to map an upstream transmissiontime window indicated in the first message according to a firsttransmission schedule of the OLT to an upstream transmission time slotaccording to a second transmission schedule of the network component,and a transmitter configured to forward the cached data in the buffer tothe OLT upon receiving the first message and send a second message thatcomprises the mapped upstream transmission time slot to the CNUs.

In yet another embodiment, the disclosure includes a method implementedby an apparatus for interconnecting a fiber-optic network and a coaxnetwork comprising receiving data from a CNU at the coax network,caching the received data in a local buffer, receiving from an OLT atthe fiber-optic network a first message that assigns an upstreamtransmission window for a specified CNU based on a first time scheduleof the OLT, and forwarding the cached data in the buffer to the OLTregardless of whether the specified CNU matches the CNU corresponding tothe cached data.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a schematic diagram of an embodiment of an EPoC system.

FIG. 2 is a schematic diagram of another embodiment of an EPoC system.

FIG. 3 is a schematic diagram of an embodiment of an EPoC system.

FIG. 4 is a schematic diagram of an embodiment of an EPoC upstreamtransmission scheme.

FIG. 5 is a schematic diagram of another embodiment of an EPoC upstreamtransmission scheme.

FIG. 6 is a flowchart of an embodiment of an EPoC upstream transmissionmethod.

FIG. 7 is a schematic diagram of an embodiment of a network unit.

FIG. 8 is a schematic diagram of an embodiment of a general-purposecomputer system.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

Multiple Ethernet over Coax (EoC) technologies and standards that havebeen used for in-home transmission have also been adapted to enableoutdoor coax access from a PON Optical Network Unit (ONU) to an EoC HeadEnd, which may be a PON OLT. Examples of such EoC technologies includeMultimedia over Coax Alliance (MoCA), the InternationalTelecommunication Union Telecommunication Standardization Sector (ITU-T)G.hn standards, the Home Phoneline Networking Alliance (HPNA), and HomePlug Audio/Video (A/V). Outdoor coax access may be enabled usingcustomer premise equipment (CPE) located at the subscriber home. The OLTmay be coupled to one or more CPEs via a corresponding CNU at the coaxnetwork side. The OLT may communicate with a plurality of CNUs via a CLTthat may be positioned between the PON and the coax network. However,these technologies may not offer end-to-end Fiber to Coax scheduling fortransferring upstream data from the CNU on the coax network to the CLTand OLT at the fiber-optic network.

Using EPON for coax cable access is being proposed by Multiple SystemOperators (MSOs) worldwide, where the EPON may be used for last fewhundred meters access for EPoC. EPON is a PON standard developed by theInstitute of Electrical and Electronics Engineers (IEEE) and specifiedin IEEE 802.3ah. EPON may provide a relatively simple and flexible wayof using optical fiber for last mile broadband service. The EPON maycomprise an OLT configured to transmit Ethernet frames at an EPON MediaAccess Control (MAC) layer. The OLT may implement a Multi-Point ControlProtocol (MPCP) that performs bandwidth assignment, bandwidth polling,auto-discovery, and ranging. Ethernet frames may be broadcasted from theOLT downstream to a plurality of ONUs based on Logical Link Identifiers(LLIDs) assigned to corresponding ONUs. The LLIDs may be embedded in thepreamble of the transmitted frames.

Typically in the EPON, upstream bandwidth for the different ONUs may beassigned by sending Gate messages from the OLT to the ONUs. The OLT maydetermine upstream transmission time windows for the ONUs by sending theONUs' LLIDs in subsequent Gate messages. Each Gate may be used to assigna transmission or polling cycle based on the MPCP. When an ONU receivesa Gate message that comprises the ONU's associated LLID, the ONU maybegin transmitting data upstream to the OLT. Similarly, other ONUs maytransmit their data upstream in turn upon receiving their LLIDs insubsequent Gate messages from the OLT. The ONUs may also send Reportmessages to the OLT to request upstream bandwidth. The Report messagesmay also comprise LLIDs that indicate the requesting ONUs. This upstreambandwidth assignment scheme may also be implemented for EPoC technology,where the Gate messages may be relayed between the OLT and the ONUs viaan EPoC network.

Disclosed herein is a system and method for improving upstream datatransmission in an EPoC based system or any other integrated PON andcoax system. The upstream data may be sent from a coax network to anEPON or other fiber based network (other PON) that is coupled to thecoax network. The system may comprise an OLT at the EPON (or PON), a CLTpositioned between the EPON (or PON) and the coax network, and one ormore CNUs coupled to one or more customer devices (or CPEs) at the coaxnetwork. The CLT may be configured to receive and cache data from theCNUs. The CLT may then forward the data in the upstream direction to theOLT upon receiving a Gate message from the OLT, regardless of whetherthe data is from the ONU associated with the LLID in the Gate message ornot. As such, the upstream data from the CNUs may be transmitted to theOLT without synchronizing upstream data transmission from the CNUs withthe OLT.

The CLT may be configured to allocate upstream transmission time slotsfor the CNUs, which may correspond to assigned time windows from the OLTthat are indicated in the Gate messages. The amount of data cached fordifferent CNUs may match the corresponding allocated time slots at theCLT. As such, the OLT may receive about the same indicated amount ofdata (or data bandwidth) per upstream transmission cycle. However, theOLT may not necessarily receive the upstream data for the CNUs at theCNU's indicated time windows in the Gate messages. Since this upstreamtransmission scheme is asynchronous, the scheme may not require timingcomponents, which may reduce cost and simplify transmissions. Further,since the CLT forwards the cached data for any CNU upstream uponreceiving a Gate message from the OLT regardless of the LLID value inthe Gate message, the data transmission cycles for the CNUs may bereduced.

FIG. 1 illustrates an embodiment of an EPoC system 100. The EPoC system100 may comprise an OLT 110 located at an EPON side, at least one CNU130 coupled to a plurality of CPEs 140 at a coax (subscriber) networkside, and a CLT 120 positioned between the OLT 110 and the CNU 130,e.g., at an EPoC between the EPON and the coax network. The OLT 110 maybe coupled via a fiber distribution network or Optical DistributionNetwork (ODN) 115 to one or more CLTs 120, and optionally to one or moreONUs (not shown), of the EPON. The fiber distribution network or ODN 115may comprise fiber optics and an optical splitter 117 that couples theOLT 110 to multiple CLTs/ONUs, including the CLT 120. The CLT 120 may becoupled to a plurality of CNUs 130 via coax cables 135 and a cablesplitter 137. Although FIG. 1 shows one CLT 120 and one CNU 130, theEPoC system 100 may comprise any number of CLTs 120 and correspondingCNUs 130. The components of the EPoC system 100 may be arranged as shownin FIG. 1 or any other suitable arrangement.

The OLT 110 may be part of the EPON and may be any device configured tocommunicate with the CNUs 130 via the CLT 120. The OLT may communicatewith one or more CLTs 120 and optionally with one or more ONUs (notshown) using optical signals transported via the fibers of the ODN 115.The OLT 110 may act as an intermediary between the CNUs 130 and anothernetwork (not shown). The OLT 110 may forward data received from theother network to the CNUs 130, and forward data received from the CNUs130 onto the other network. Although the specific configuration of theOLT 110 may vary depending on the type of PON or EPON, in an embodiment,the OLT 110 may comprise a transmitter and a receiver. When the othernetwork is using a network protocol that is different from the protocolused in the EPON, the OLT 110 may comprise a converter that converts theother network protocol into the EPON protocol. The OLT converter mayalso convert the EPON protocol into the other network protocol.

The CLT 120 may be any device or component configured to forwarddownstream data from the OLT 110 to the corresponding CNUs 130 andforward upstream data from the CNUs 120 to the OLT 110. The CLT 120 mayconvert the downstream and upstream data appropriately to transfer thedata between the optical fiber and the coax cable. The data transferredover the fiber (of the ODN 115) may be transmitted or received in theform of optical signals, and the data transferred over the coax cables135 may be transmitted or received in the form of electrical signals.The CLT 120 may also encapsulate or frame the data in the fiber-opticnetwork side and coax network side differently. The CLT 120 may comprisea storage medium (e.g., a hard drive or memory) that acts as a cache (orbuffer) for caching upstream data from the CNUs 130 to the OLT 110. TheCLT 120 may dedicate an upstream data cache 125 for the CNUs 130, whichmay be any suitable portion of the storage medium or memory.

The CNUs 130 may be any devices configured to transport data between theCLT 120 and the corresponding CPEs 140. The CNU 130 may combine the datafrom a plurality of corresponding CPEs 140 (e.g., at the same home) andsend the data upstream to the CLT 120. The CNU 130 may also receive datafrom the CLT 120 and distribute the data downstream to the correspondingCPEs 140. Examples of the CNUs 130 include set top boxes, home(wireless) routers, and modems. The CPEs 140 may be any wired orwireless communications device or component that may be used to receiveand send data, such as computer desktops, laptops, tablets, phones, andsmartphones. In other embodiments, the OLT 110, CLT 120, and CNUs 130described above may be part of any integrated PON and coax network otherthan the EPoC, where the PON may be any PON other than an EPON, such asa Gigabit PON (GPON) or another type of TDM PONs.

In the case of upstream data transmissions, the CLT 120 may cache thedata received from any of the CNUs 130 at the upstream data cache 125before forwarding the data upstream to the OLT 110. The CLT 120 mayforward the cached data from the upstream data cache 125 after receivinga Gate message from the OLT 110 without matching the forwarded data tothe LLID in the Gate message. The cached data may be forwarded upstreamregardless of the indicated LLID from the OLT 110 and may or may notcorrespond to the CNU 130 associated with the LLID in the Gate message.This may remove the synchronization of upstream transmissions betweenthe coax network and the fiber-optic network, which may simplifycommunications and reduce cost. Further, since the CNU's upstream datamay be forwarded from the CLT upon receiving any Gate message, the CNU'scached data may be forwarded before receiving the CNU's intended Gatemessage. Thus, the CNU's cached data may be transmitted upstream withreduced delay, which may reduce the upstream data transmission cycle forthe CNU.

FIG. 2 illustrates another embodiment of an EPoC system 200. The EPoCsystem 200 may comprise an OLT 210 (e.g., at an EPON side), a CNU 230(at a coax network side), and a CLT 220 positioned between the OLT 210and the CNU 230. The OLT 210, CLT 220, and CNU 230 may be configuredsimilar to the OLT 110, CLT 120, and CNU 130, respectively. The OLT 210may be configured to assign an upstream data transmission time windowfor each CNU 230 according to the MPCP. The upstream data may bereceived by the OLT 210 at an EPON MAC (or physical) layer. The CLT 220may comprise a plurality of upstream data caches 225 for cachingupstream data from the CNUs 230, which may have different assignedpriority levels. The upstream data caches 225 may be used for cachingdifferent priority of data frames from the CNUs 230. For instance, thedata frames from the CNUs 230 may comprise MPCP (control) frames thatmay have high priority, voice frames that may have medium priority, andother data frames that may have low priority. The different prioritydata frames may be cached in corresponding caches 225, such as in a MPCPframe cache, a voice frame cache, and a data frame cache, respectively.

The OLT 210 may send a Gate message to the CLT 220 to assign an upstreamdata transmission time window for one or more CNU 230. The CLT 220 mayprocess the Gate message to map a corresponding upstream transmissiontime slot to one or more CNU 230, which may include the same ordifferent CNUs 230 than indicated in the Gate message. The CLT 220 mayallocate one or more upstream transmission time slots to one or moreCNUs 230 that may be about equal to the upstream data transmission timewindow indicated in the Gate message. However, the upstream transmissiontime slot(s) may be assigned or scheduled differently in time than thetime schedule of the OLT 210. The CLT 220 may send the mapped upstreamtransmission time slot(s) to the corresponding CNU(s) 230 using a coaxmessage, which may be broadcast to the CNUs 230. Any type of suitablemessage in the coax network that indicates the mapped upstreamtransmission time slot(s) to the CNUs is referred to herein as a Mapmessage. Hence, for each received Gate message from the OLT, a coax Mapmessage may be sent to the corresponding CNU(s) 230. The CNUs 230 maythen send the upstream data according to the CNUs' assigned upstreamtransmission time slots.

The CLT 220 may allocate the upstream data transmission time slots forthe different CNUs according to a local time scheduling of the CLT 220,which may be independent from the OLT's time scheduling. For example,the upstream data transmission time slots may be allocated to the CNUsaccording to the schedule of cached data at the CLT 220 from thedifferent CNUs 230, where for higher priority received and cached datamay be scheduled first. Thus, the cached data may be forwarded to theOLT 210 from the higher priority upstream data caches 225 first, e.g.,as long as the amount of forwarded data matches the assigned time slots.This may also decouple the scheduling of upstream data transmissionsfrom the OLT's assigned schedule for upstream data transmissions. Asdescribed above, the upstream data transmission bandwidths from the OLT210 may still be preserved, since the time slots assigned by the CLT 220may be about equal to the time windows assigned by the OLT 210.

FIG. 3 illustrates another embodiment of an EPoC system 300. The EPoCsystem 300 may comprise an OLT 310, a CLT 320, and a plurality of CNUs330, which may be configured as described above. The OLT 310 may use theMPCP with dynamic bandwidth allocation (DBA), to schedule upstream datatransmissions for the CNUs 330. Specifically, the OLT 310 may send aplurality of Gate messages that indicate a plurality of LLIDs anddesignated time windows for the corresponding CNUs 330. The Gatemessages may be sent subsequently from the OLT 310 to the CLT 320according to the OLT's determined schedule for upstream datatransmissions from the CNUs 330. The MPCP scheduling at the OLT 310 maybe implemented with DBA, where the OLT 310 may reschedule the upstreamdata transmissions for the CNUs 330 by resending additional Gatemessages to accommodate to changing fiber-optic network (e.g., EPON)conditions, such as changes in available bandwidth, failures, or trafficcongestion.

Upon receiving each Gate message from the OLT 310, the CLT 320 may alsouse the MPCP with DBA to schedule upstream data transmissions for theCNUs 330 based on the designated time windows in the Gate messages. TheCLT 320 may map the time windows for the CNUs 330 to corresponding timeslots to reschedule the upstream data transmissions for the CNUs 330.Specifically, the CLT 320 may map each time window for each CNU 330 to acomparable amount of time slots according to the CLT's determinedschedule for upstream data transmissions from the CNUs 330. The CLT'sschedule may be based on cached data conditions (and optionally otherlocal CLT or coax network resource conditions), such as the order andamount of cached data from the different CNUs 330. The CLT 320 may senda plurality of Map messages that indicate the designated time slots (andLLIDs) for the corresponding CNUs 330. The Map messages may be sent fromthe CLT 320 to the CLTs 320 after or upon receiving the correspondingGate messages from the OLT 310. The Map messages may indicate time slotsfor the corresponding CNUs 330 that may be about equal to the indicatedtime windows in the Gate messages for the CNUs 330. However, the Mapmessages may indicate a different order for upstream transmissions fromthe CNUs 330 than indicated in the Gate messages.

For example, the OLT 310 may send to the CLT 320 subsequent Gatemessages that indicate the LLID values, LLID1, LLID3, and LLID2, forthree corresponding CNUs 330, CNU1, CNU3, and CNU2, respectively, toschedule upstream data transmissions in that order according to the OLT's schedule. Hence, the CLT 320 may transmit three correspondingsubsequent Map messages for CNU1, CNU2, and CNU3, respectively, toschedule upstream data transmissions in that modified order according tothe CLT's schedule. The CLT 320 may send one Map message at a time foreach received Gate message.

Each of the CNUs 330 may return upstream data to the CLT 320 accordingto the designated time slots in the received Map messages. The CLT 320may cache the data, e.g., for some time, and subsequently send thecached data upstream to the OLT 310 upon receiving a Gate messageregardless of the LLID indicated in the Gate message, as describedabove. The cached data may be sent upstream to the OLT 310 in the orderthe data was received and cached from the CNUs 330, such as on a firstin first out (FIFO) basis. This order may correspond to the CLT'sscheduled and indicated time slots in previously sent Map messages tothe CNUs 330. The CLT 320 may send upstream cached data corresponding toone Map message at a time upon receiving each Gate message.

FIG. 4 illustrates an embodiment of an EPoC upstream transmission scheme400, which may be implemented in the EPoC systems described above. TheEPoC upstream transmission scheme 400 may be implemented by an OLT 410,a CLT 420, and a plurality of CNUs 430, which may be configured asdescribed above. Initially, the OLT 410 may send to the CLT 420 a Gatemessage that indicates a LLID for one of the CNUs 430, e.g., LLID3 forCNU3. Upon receiving the Gate message, the CLT 420 may generate a Mapmessage corresponding to the Gate message, as described above, and sendthe Map message to the same CNU 430, CNU3. The Map message may alsoindicate the CNU's LLID, LLID3.

The CLT 420 may also respond to the Gate message by forwarding data(e.g., one or more packets) that may be previously received and cachedat the CLT 420, without matching the data to the LLID (LLID3) in thereceived Gate message. For instance, the CLT 420 may forward to the OLT410 the cached data or packets for other CNUs 430, CNU1 and CNU2, thatare not indicated in the Gate message. The packets or data forwardedupstream may be previously assigned corresponding time slots andreceived by the CLT 420 using previously sent Map messages to thecorresponding CNUs 430 (CNU1 and CNU2). The forwarded packets maycomprise the LLIDs of the CNUs 430 to indicate the corresponding CNUs,e.g., LLID1 for CNU1 and LLID2 for CNU2. This may enable the OLT 410 todistinguish the data received from different CNUs 430.

After receiving the Map message from the CLT 420, the intended CNU 430(CNU3) may respond by sending an amount or size of data (e.g., a numberof packets) that matches the assigned time slot indicated in the Mapmessage from the CLT 420. The CLT 420 may receive the data and cache thedata. The received packets may comprise the sending CNU's LLID, e.g.,LLID3 for CNU 3. The CLT 420 may subsequently forward the data for theCNU 430 from the cache when a subsequent Gate message is received,regardless of whether the Gate message indicates the CNU's LLID (LLID3)or another LLID for another CNU 430.

FIG. 5 illustrates another embodiment of an EPoC upstream transmissionscheme 500, which may be implemented in the EPoC systems describedabove. The EPoC upstream transmission scheme 500 may be implemented byan OLT 510, a CLT 520, and a plurality of CNUs 530, which may beconfigured as described above. Initially, the OLT 510 may send to theCLT 520 a Gate message that indicates a LLID for one of the CNUs 530,e.g., LLID3 for CNU3. Upon receiving the Gate message, the CLT 520 maygenerate a Map message corresponding to the Gate message, as describedabove, and send the Map message to the same CNU 530 (CNU3). The Mapmessage may also indicate the CNU's LLID, LLID3.

At this point, the CLT's cache may be empty or may not comprise receiveddata from any of the CNUs 530. Thus, the CLT 520 may not forward any CNUdata to the OLT 510 upon receiving the Gate message. After receiving theMap message from the CLT 520, the indicated CNU 530 (CNU3) may respondby sending an amount of data that matches the assigned time slotindicated in the Map message from the CLT 520. The CLT 520 may receivethe data and cache the data. The received packets may comprise thesending CNU's LLID, e.g., LLID3 for CNU3. Since, the CLT 520 hasreceived the CNU's data after some time delay from receiving the Gatemessage from the OLT 510, the CLT 520 may not forward the CNU's cacheddata and instead wait for another Gate message for a next transmissioncycle to arrive from the OLT 510. An OLT transmission cycle maycorrespond to the time window between two transmitted Gate messages. Inthis situation, the buffer (or cache) at the CLT 520 that holds suchdata is referred to herein as a dead frame buffer.

To forward the cached data and empty the dead frame buffer (instead ofwaiting for a next Gate message for the next cycle), the CLT 520 maysend a Report message to the OLT 510 to request additional time toforward the cached CNU data. This may be desirable to avoid thesituation of receiving subsequent data from the CNUs 530 and overloadingthe buffer at the CLT 520 before receiving the next Gate message formthe OLT 510. The CLT 520 may comprise a buffer monitor timer 522 thatmay be started upon receiving a Gate message. When the timer expiresafter a determined buffer wait time, such as equal to one or two pollingcycles of the OLT 510, the CLT 510 may send the Report message to theOLT 510 to extend the time window for transmitting upstream data (beforeexchanging a next Gate message). The CLT 520 may then forward the cacheddata to the OLT 510. The CLT 520 may send the Report message and forwardthe cached data before receiving the next Gate message if the buffermonitor timer 522 expires before be the next transmission cycle.Otherwise, the CLT 510 may wait until receiving the next Gate messagebefore forwarding the cached data. By extending the time window andtransmitting the cached data in the dead frame buffer, the scheme 500may avoid wasting or skipping one transmission cycle without sending anydata to the OLT 510. Thus, the scheme 500 may improve bandwidthutilization and further reduce the CNU' s upstream data transmissioncycle (in the case of a dead frame buffer situation).

FIG. 6 illustrates an embodiment of an EPoC upstream transmission method600, which may be implemented in the EPoC systems and schemes describedabove. The EPoC upstream transmission method 600 may be implemented by aCLT that may be coupled to and in communications with an OLT and one ormore CNUs. The CLT, OLT, and CNUs may be configured as described above.The method 600 may begin at block 602, where a Gate message may bereceived from an OLT. The CLT may receive from the OLT the Gate messagethat comprises a LLID indicating a CNU. At block 604, a Map message maybe sent to one or more CNUs. Upon receiving the Gate message form theOLT, the CLT may map the time window indicated in the gate message toone or more time slots for one or more CNUs. The time slot(s) of the Mapmessage and the time window of the Gate message may correspond to aboutthe same time period. The CLT may send a Map message to one or more CNUsindicating the mapped time slot and the LLID for each CNU.

At block 606, the method 600 may verify whether a data buffer (for theCLT) is empty. If the condition of block 606 is true, then the method600 may proceed to block 614. Otherwise, the method 600 may proceed toblock 608. At block 608, the cached data (in the buffer) may beforwarded to the OLT. The CLT may forward to the OLT the cached data inthe buffer, which may be packets for one or more CNUs. At block 610,data may be received from the CNU(s). The CLT may receive one or morepackets from one or more CNUs, e.g., to which the Map messages weresent. At block 612, the data may be cached in the buffer. The CLT maycache the received data until a next Gate message is received. Themethod 600 may then return to block 602, where a next Gate message isreceived.

At block 614, a buffer monitor timer may be started. The CLT may startthe buffer monitor timer to avoid the dead frame buffer situationdescribed above (in scheme 500). At block 616, data from the CNU(s) maybe received. The CLT may receive one or more packets from one or moreCNUs, e.g., to which the Map messages were sent. At block 618, the datamay be cached in the buffer. At block 620, the method 600 may verifywhether the buffer monitor timer has expired. For instance, the buffermonitor timer may be set to one or two transmission or polling cycles ofthe OLT. If the condition of block 620 is true, then the method 600 mayproceed to block 622. Otherwise, the method 600 may return to block 602,where a next Gate message is received before the buffer monitor timerexpires. At block 622, a Report message may be sent to the OLT. The CLTmay send the Report message to the OLT to extend the time window for thecurrent transmission or polling cycle and empty the dead frame bufferbefore the next polling cycle. At block 624, the cached data (in thebuffer) may be forwarded to the OLT. The method 600 may then return toblock 602, where a next Gate message is received.

FIG. 7 illustrates an embodiment of a network unit 700, which may be anydevice that transports and processes data through an EPoC system, suchas the EPoC systems 100 and 200. For instance, the network unit 700 maybe located in any of the network components described above, e.g., atthe OLT, CLT, or CNU. The network unit 700 may comprise one or moreingress ports or units 710 coupled to a receiver (Rx) 712 for receivingsignals and frames/data from other network components. The network unit700 may comprise a logic unit 720 to determine which network componentsto send the packets to. The logic unit 720 may be implemented usinghardware, software, or both. The network unit 700 may also comprise oneor more egress ports or units 730 coupled to a transmitter (Tx) 732 fortransmitting signals and frames/data to the other network components.The receiver 712, logic unit 720, and transmitter 732 may also implementor support any of the transmission schemes and methods described above.The components of the network unit 700 may be arranged as shown in FIG.7.

The network components described above may be implemented on anygeneral-purpose network component, such as a computer or networkcomponent with sufficient processing power, memory resources, andnetwork throughput capability to handle the necessary workload placedupon it. FIG. 8 illustrates a typical, general-purpose network component800 suitable for implementing one or more embodiments of the componentsdisclosed herein. The network component 800 includes a processor 802(which may be referred to as a central processor unit or CPU) that is incommunication with memory devices including secondary storage 804, readonly memory (ROM) 806, random access memory (RAM) 808, input/output(I/O) devices 810, and network connectivity devices 812. The processor802 may be implemented as one or more CPU chips, or may be part of oneor more application specific integrated circuits (ASICs).

The secondary storage 804 is typically comprised of one or more diskdrives or tape drives and is used for non-volatile storage of data andas an over-flow data storage device if RAM 808 is not large enough tohold all working data. Secondary storage 804 may be used to storeprograms that are loaded into RAM 808 when such programs are selectedfor execution. The ROM 806 is used to store instructions and perhapsdata that are read during program execution. ROM 806 is a non-volatilememory device that typically has a small memory capacity relative to thelarger memory capacity of secondary storage 804. The RAM 808 is used tostore volatile data and perhaps to store instructions. Access to bothROM 806 and RAM 808 is typically faster than to secondary storage 804.

At least one embodiment is disclosed and variations, combinations,and/or modifications of the embodiment(s) and/or features of theembodiment(s) made by a person having ordinary skill in the art arewithin the scope of the disclosure. Alternative embodiments that resultfrom combining, integrating, and/or omitting features of theembodiment(s) are also within the scope of the disclosure. Wherenumerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example,whenever a numerical range with a lower limit, R₁, and an upper limit,R_(u), is disclosed, any number falling within the range is specificallydisclosed. In particular, the following numbers within the range arespecifically disclosed: R=R₁+k*(R_(u)−R₁), wherein k is a variableranging from 1 percent to 100 percent with a 1 percent increment, i.e.,k is 1 percent, 2 percent, 3 percent, 4 percent, 7 percent, . . . , 70percent, 71 percent, 72 percent, . . . , 97 percent, 96 percent, 97percent, 98 percent, 99 percent, or 100 percent. Moreover, any numericalrange defined by two R numbers as defined in the above is alsospecifically disclosed. Use of the term “optionally” with respect to anyelement of a claim means that the element is required, or alternatively,the element is not required, both alternatives being within the scope ofthe claim. Use of broader terms such as comprises, includes, and havingshould be understood to provide support for narrower terms such asconsisting of, consisting essentially of, and comprised substantiallyof. Accordingly, the scope of protection is not limited by thedescription set out above but is defined by the claims that follow, thatscope including all equivalents of the subject matter of the claims.Each and every claim is incorporated as further disclosure into thespecification and the claims are embodiment(s) of the presentdisclosure. The discussion of a reference in the disclosure is not anadmission that it is prior art, especially any reference that has apublication date after the priority date of this application. Thedisclosure of all patents, patent applications, and publications citedin the disclosure are hereby incorporated by reference, to the extentthat they provide exemplary, procedural, or other details supplementaryto the disclosure.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. An apparatus for interconnecting a fiber-opticnetwork and a coax network, comprising: a coax line terminal (CLT)configured to couple to an optical line terminal (OLT) at thefiber-optic network and a plurality of coax network units (CNUs) at thecoax network and to cache data received from the CNUs and forward thecached data to the OLT upon receiving a message from the OLT thatassigns a transmission cycle for a specified CNU, wherein the CLTforwards the cached data to the OLT upon receiving the messageregardless of whether the cached data corresponds to the specified CNU.2. The apparatus of claim 1, wherein the CLT is further configured toassign a plurality of upstream transmission time slots to the CNUs thatare comparable to a plurality of upstream transmission time windowsassigned from the OLT for the same CNUs to achieve asynchronous upstreamtransmissions between the fiber-optic network and the coax network. 3.The apparatus of claim 1, wherein the CLT comprises a plurality ofcaches for caching a plurality of different priority data frames, andwherein the CLT forwards the different priority data frames from thecorresponding caches upon receiving the message from the OLT based onpriority regardless whether the data frames correspond to the specifiedCNU in the message.
 4. The apparatus of claim 1, wherein the fiber-opticnetwork is an Ethernet passive optical network (EPON), and wherein themessage is a Gate message that assigns a polling cycle for the specifiedCNU based on a Multi-Point Control Protocol (MPCP).
 5. The apparatus ofclaim 4, wherein the Gate message comprises a Logical Link Identifier(LLID) that indicates the specified CNU, and wherein the CLT forwardsthe cached data to the OLT without matching the LLID to the cached data.6. The apparatus of claim 4, wherein the CLT is further configured tomap the Gate message to a Map message that assigns a comparable upstreamtransmission time window as the Gate message and broadcast the Mapmessage to the CNUs.
 7. The apparatus of claim 6, wherein the CLTassigns one or more time slots that match the upstream transmission timewindow to one or more of the CNUs that are indicated in the Map messageusing one or more corresponding LLIDS.
 8. The apparatus of claim 1,wherein the CLT is further configured to use a buffer monitor timer toforward CNU cached data at the CLT during a polling cycle for the OLT,wherein the CNU cached data is received at the CLT after receiving themessage from the OLT.
 9. A network component for interconnecting afiber-optic network with a coax network in a passive optical network(PON) over coax system comprising: a receiver configured to receive datafrom one or more coax network units (CNUs) in the coax network and afirst message from an optical line terminal (OLT) of the PON thatindicates a specified CNU; a buffer configured to cache the receiveddata; a processor configured to map an upstream transmission time windowindicated in the first message according to a first transmissionschedule of the OLT to an upstream transmission time slot according to asecond transmission schedule of the network component; and a transmitterconfigured to forward the cached data in the buffer to the OLT uponreceiving the first message and send a second message that comprises themapped upstream transmission time slot to the CNUs.
 10. The networkcomponent of claim 9, wherein the buffer comprises a plurality of cachesfor caching a plurality of different priority data frames, and whereinthe different priority data frames are forwarded from the correspondingcaches upon receiving the first message from the OLT based on priorityregardless whether the data frames correspond to the specified CNU inthe first message.
 11. The network component of claim 9, wherein thecached data is received from a different CNU than the specified CNU. 12.The network component of claim 9, wherein the time slot is assigned tothe specified CNU and is indicated in the second message using a LogicalLink Identifier (LLID) associated with the specified CNU.
 13. Thenetwork component of claim 9, wherein the second transmission scheduleof the network component assigns a plurality of time slots for the CNUsthat do not overlap with a plurality of time windows in the firstschedule of the OLT that are assigned to the same CNUs.
 14. The networkcomponent of claim 13, wherein the time slots of the second schedulethat are assigned to the CNUs are about equal to the time windows of thefirst schedule that are assigned to the same CNUs.
 15. The networkcomponent of claim 9 further comprising a buffer monitor timerconfigured to determine an amount of wait time after receiving a firstmessage, wherein the buffer monitor timer is triggered upon receivingthe first message if the buffer is empty of data from the CNUs.
 16. Thenetwork component of claim 15, wherein the transmitter is furtherconfigured to forward any data that is cached in the buffer and receivedfrom the CNUs to the OLT after receiving the first message if the buffermonitor timer expires before receiving a next first message.
 17. Amethod implemented by an apparatus for interconnecting a fiber-opticnetwork and a coax network comprising: receiving data from a coaxnetwork unit (CNU) at the coax network; caching the received data in alocal buffer; receiving from an optical line terminal (OLT) at thefiber-optic network a first message that assigns an upstreamtransmission window for a specified CNU based on a first time scheduleof the OLT; and forwarding the cached data in the buffer to the OLTregardless of whether the specified CNU matches the CNU corresponding tothe cached data.
 18. The method of claim 17, wherein the local buffercomprises a plurality of caches for caching a plurality of differentpriority data frames, and wherein the different priority data frames areforwarded from the corresponding caches upon receiving the first messagefrom the OLT based on priority regardless whether the data framescorrespond to the specified CNU in the first message.
 19. The method ofclaim 17 further comprising: mapping the upstream transmission window toa comparable upstream transmission time slot based on a second timeschedule for the coax network; and sending to the coax network a secondmessage that assigns the upstream transmission time slot to thespecified CNU.
 20. The method of claim 17 further comprising: receivingfrom the OLT a second message that assigns an upstream transmissionwindow; starting a buffer monitor timer upon receiving the secondmessage from the OLT if the local buffer is empty of data from the coaxnetwork; receiving subsequent data from the coax network; caching thesubsequent data from the coax network in the local buffer; sending athird message to the OLT to request extending the upstream transmissionwindow; and forwarding the cached subsequent data to the OLT if thebuffer monitor timer expires before receiving from the OLT a nextmessage that assigns an upstream transmission window.
 21. The method ofclaim 20, wherein the buffer monitor timer is set up to expire afterabout one or about two Multi-Point Control Protocol (MPCP) pollingcycles determined by the OLT.
 22. The method of claim 20, wherein thefirst message, the second message, and the next message are Ethernetpassive optical network (EPON) MPCP Gate messages, and wherein the thirdmessage is an EPON MPCP Report message.